Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$55.68	6.111%	$59.0826	$59.08	$59.10	$59.10
Purchase #2	$128.74	3.363%	$133.0695	$133.07	$133.05	$133.10
Purchase #3	$127.42	9.723%	$139.809	$139.81	$139.80	$139.80
Purchase #4	$161.58	3.590%	$167.3807	$167.38	$167.40	$167.40
Purchase #5	$93.51	9.227%	$102.1382	$102.14	$102.15	$102.10
Purchase #6	$93.62	8.388%	$101.4728	$101.47	$101.45	$101.50
Purchase #7	$140.31	4.535%	$146.6731	$146.67	$146.65	$146.70
7 purchase totals =	$800.86		$849.6259	$849.62	$849.60	$849.70